1. Field
Various features pertain to switching between wireless radio communication systems and more particularly, to a method and device that preserves a current session context when retrying a service on a different radio access technology.
2. Background
A multi-mode user equipment (UE), e.g., mobile communication device, may be capable of operating according to two or more different radio access technologies, such as through packet-switched networks (e.g., a network compliant with a Long Term Evolution (LTE) air interface standard) and circuit-switched networks (e.g., a 1xRTT core CDMA2000 wireless air interface standard). During operation, the UE may register with the packet-switched network, setup a connection or link, and establish a data communication session over an IP Multimedia Subsystem (IMS) (on an LTE compatible network) which it can use for various types of services. For example, the UE may be configured to implement Short Message Service (SMS) services or other applications such as voice communications while operating over an LTE packet-switched network.
In general, LTE packet-switched networks provide centralized control of many UE operations. When the UE is operating in an LTE packet-switched network (i.e., after a successful IMS Registration), it is expected that the UE remain on the LTE packet-switched network for all services or applications. When the user tries to send a mobile originated (MO) service (e.g., SMS), the UE attempts to deliver the service data or messages via the IMS core of the packet-switched network. If the service is unavailable, the UE may receive an error message from the IMS core that is indicative of some error in the service delivery over the IMS plane.
The multi-mode UE may be capable of switching its serving or active radio access technology to implement the service (e.g., SMS) directly over a circuit-switched (CS) network/domain (e.g., 1xRTT, GERAN, UTRAN). That is, the UE may switch from its LTE interface to, for example, a 1xRTT interface to retry sending the service data or messages. However, in LTE packet-switched networks, the LTE network controls the connection or link established with the UE. That is, the LTE network operates under the assumption that the UE will continue to communicate over the LTE packet-switched network. Therefore, the UE cannot simple abandon its connection or link with the LTE packet-switched network without losing incoming pages on LTE air interface.
Therefore, a procedure is needed to execute inter-radio access technology (RAT) retries for certain services in a manner that is transparent to the UE (“silent redial”) and does not result in data loss or context loss for the UE over the LTE packet-switched network.